Mitigate permissions loss in Table ACLs by running appliers with sing…

…le thread (#518)

src/databricks/labs/ucx/framework/parallel.py

@@ -27,10 +27,13 @@ def __init__(self, name, tasks: list[Callable[..., Result]], num_threads: int):
         self._default_log_every = 100
 
     @classmethod
-    def gather(cls, name: str, tasks: list[Callable[..., Result]]) -> (list[Result], list[Exception]):
-        num_threads = os.cpu_count() * 2
-        if num_threads < MIN_THREADS:
-            num_threads = MIN_THREADS
+    def gather(
+        cls, name: str, tasks: list[Callable[..., Result]], num_threads: int | None = None
+    ) -> (list[Result], list[Exception]):
+        if num_threads is None:
+            num_threads = os.cpu_count() * 2
+            if num_threads < MIN_THREADS:
+                num_threads = MIN_THREADS
         return cls(name, tasks, num_threads=num_threads)._run()
 
     def _run(self) -> (list[Result], list[Exception]):

src/databricks/labs/ucx/workspace_access/manager.py

@@ -118,7 +118,9 @@ def apply_group_permissions(self, migration_state: GroupMigrationState, destinat
             applier_tasks.extend(tasks_for_support)
 
         logger.info(f"Starting to apply permissions on {destination} groups. Total tasks: {len(applier_tasks)}")
-        _, errors = Threads.gather(f"apply {destination} group permissions", applier_tasks)
+        # run with 1 thread to temp bugfix TableACL grants issue in the platform
+        # see: https://databricks.atlassian.net/browse/ES-908737
+        _, errors = Threads.gather(f"apply {destination} group permissions", applier_tasks, num_threads=1)
         if len(errors) > 0:
             # TODO: https://github.com/databrickslabs/ucx/issues/406
             logger.error(f"Detected {len(errors)} while applying permissions")